Engaging The Chosen Assassin safely

How can I engage combat with The Chosen Assassin without taking damage?

The Assassin seems to often begin combat (including her first story mission debut) cloaked, being all but completely undetectable until she attacks. She is also often immune to Overwatch fire both before and after being revealed. Therefore, it seems impossible, or at least implausible, to engage her before she attacks at least once. Her attacks are also highly accurate (if they obey the same rules as her sword loot drop, they are always 100% and cannot miss).

This attack can be dangerous, dealing serious damage or even leading to an instant-kill. As such, I would want to avoid taking any hits at all. However, I do not see how that is possible. Are there any ways to deal with The Assassin without letting her attack you first? Alternatively, are there reliable ways to defend against the first attack?

Possible ideas:

• Shooting explosives or flashbangs toward random areas where she might be (Implausible, unlikely, and wasteful).
• Using Hunker Down (may or may not work, depending on the accuracy of the attack).

Solution 1:

There are three simple solutions available to you.

• Battle Scanner - Unlocked as part of the Advent Trooper autopsy. Battle Scanners will reveal all concealed units, including disguised Faceless, burrowed Chyrssalids, or the Assassin herself, works through walls, and is thrown like a grenade.
• Scanning Protocol - Available to Sergeant+ ranked Specialists, this provides the same functionality as the Battle Scanner, though it cannot be thrown.
• Flanking - Your last resort option --If you suspect the Assassin is nearby, you can move your soldiers to the far side of cover, to attempt to visually identify the Assassin. Just like your soldiers lose concealment when flanked, so too can you break the Assassin's stealth by achieving a flanking L.o.S., revealing her for everyone.